The present invention relates to the breaking of rock and concrete slabs in situ into pieces small enough to remove by conventional earth moving equipment and more particularly to an improved apparatus to accomplish the same.
In the past, large rocks were split or cracked by the use of dynamite. This same technique can be employed with concrete slabs. When dynamite was used, it was necessary to drill bore holes in the rock into which a stick of dynamite was placed. An electric cap is attached to the stick of dynamite with the wires feeding therefrom connected in a circuit containing a switch and a source of electricity.
One of the drawbacks to using dynamite to split or crack large rocks and concrete slabs is the danger factor. If the blasting operation is to be performed in an area having building or homes in close proximity, it is necessary to cover the rock with a blasting mat to prevent propulsion of pieces of rock through the air in an uncontrolled manner. Special risks are created where the blasting operation takes place near gas lines. Also if dynamite is being used a special magazine is needed to store or carry the dynamite to the job site. The result of the danger necessitates the obtaining of special permits to perform the blasting operations and also necessitates costly liability insurance. Liability insurance premiums are a prime factor in the high cost of conventional explosive use.
A further drawback to the use of dynamite to split large rocks and concrete slabs in an area having building or homes in close proximity is due to the shock waves generated which travel along the rock ledge which can produce cracks in foundations of nearby homes, can crack well casings for on site artesian wells and can crack on site or home maintained septic systems. Thus, the home can be damaged and the artesian well can be polluted by cracks developed in the well casing and in septic systems on the home site.
Another drawback to the use of dynamite to split large rocks and concrete slabs is that it requires a trained expert to set the charge and explode it. In many cases this necessitates the hiring of a blasting contractor and delays may result from his having to fit your job into his schedule. Also special time consuming procedures are normally observed to insure safety and one of these is the requirement of removing personnel and/or equipment to a safer place while the blasting operation takes place. This in general results in production down time since the general work of the labor force is normally curtailed while the blasting process takes place.
A further drawback to the use of dynamite as opposed to a machine or tool that will perform the same result is the cost factor. The blasting caps required as well as the dynamite itself required to provide a useful force is expensive. Once the blasting operation occurs, these materials are lost and cannot be used again. If a tool or machine is utilized to perform the operation, it can normally be used again and again.
An additional drawback to the use of explosives for cracking or splitting of large rocks and concrete slabs is the relatively long time required to perform the preparation work. The charges are normally set in holes which have been drilled approximately four feet deep into the rock. The time required for drilling the first two feet of the hole takes about four minutes. To perform the next two feet of drilling requires more than twice that amount of time. One reason for this is the loss of hammering power due to the dampening effect on the longer shaft. An additional factor is the loss of sufficient air volume and pressure to exhaust chips from the bottom of the hole resulting in loss of drilling efficiency due to the padding effect caused by the chips that are not removed quickly enough. When long drilling time of these holes is multiplied times the number of holes that will be drilled in cracking a large rock, the total time becomes very substantial.
A final drawback to the use of dynamite for splitting large rocks is the environmental aspect. The use of dynamite results in the release of poisonous gases into the air. It also results in dust being stirred up into the atmosphere.
Machines or tools to break rock and concrete slabs are known in the prior art. The prior art uses a wedge having two tapered surfaces which is driven between two feathers or pressure cheeks which can be inserted in predrilled holes and the pressure cheeks or feathers are laterally moved by the longitudinal movement of the two surfaced tapered wedge.
Nine U.S. patents to H. DARDA of Germany have employed a hydraulic cylinder to move a wedge between two held feathers. These patents include U.S. Pat. Nos. 3,414,328; 3,439,954; 3,488,093; 3,526,434; 3,791,698; 3,883,178; 3,894,772; 3,957,309 and 3,995,906. In addition, patents of note are U.S. Pat. No. 2,093,452 issued to JOY as well as U.S. Pat. Nos. 3,550,191 and 3,572,840 issued to FLETCHER and U.S. Pat. No. 4,114,951 issued to LANGFIELD ET AL.
One disadvantage of the above prior art is that the steel thrust or wear plate employed in these apparatus often cracks or breaks during or as a result of the thrust and splitting action movement of the two surfaced tapered wedge. These wear or thrust plates are retained by grooves and/or screws. Under this thrusting action and when and where dirt, rock or other material or factors reduce the ability of the wedge to slide along the face of the feathers an increase of pressure and a cracking or breaking of these wear plates results. Repeated actuation of the wedge to produce this splitting action often causes cracked or broken wear or thrust plates to cut or mutilate the housing or retainer, usually made of aluminum, to the extent that it is not satisfactorily useable.
All of the prior art known uses hydraulic or air pressure (fluid pressure) to power a mechanical device. Virtually all the prior art uses the same principle, namely, the transfer of longitudinal power through the mechanical advantage of a tapered wedge having two tapered surfaces to lateral power exterted upon the sides of predrilled holes in rock or concrete slabs.
The prior art apparatus is able to generate forces of less than one million pounds per square inch which is far below the forces needed to break granite and trap rock. As a result of this, the state of the art apparatus necessarily limits its use to the breaking of concrete slabs, softer rock and minerals.
A majority of the prior art apparatus uses wedges having a mechanical advantage of approximately 10 to 1. This prior art apparatus must do so for a number of reasons; (1) holes drilled in rock vary in the size of diameter of the drilled holes into which the feathers must fit, (2) when the holes are drilled they are not drilled straight and the feathers cannot be made too long or breakage results.
Devices of the prior art can only increase power in one of three basic ways (1) increase power of the hydraulic ram by (a) increasing the pressure over 7,100 psi which is really not feasible, (b) increase the size of the hydraulic cylinder which results in a subsequent increase in bulk and unmanageability; (2) change the mechanical advantage over 10 to 1 by making the wedge thinner relative to length which increases the stroke length, or making the wedge longer which also increases the stroke length. With both of these remedies there is required a corresponding increase in the predrilled hole length. Most of the problems in the prior art occur because of the requirement of deep holes. To double the power to 20 to 1 mechanical advantage requires doubly the length of the hole that is predrilled in the rock.